Ann Lab Med 2017; 37(5): 434-437  https://doi.org/10.3343/alm.2017.37.5.434
Identification of viridans streptococci With Matrix-Assisted Laser Desorption & Ionization Time-of-flight Mass Spectrometry by an In-house Method and a Commercially Available System
Catalina-Suzana Stingu, M.D.1, Klaus Eschrich, Ph.D.2, Juliane Thiel, M.D.1, Toralf Borgmann, M.D.1, Reiner Schaumann, M.D.1, and Arne C. Rodloff, M.D.1
Institute for Medical Microbiology and Epidemiology of Infectious Diseases1, University Hospital, University of Leipzig; Rudolf-Schoenheimer-Institute for Biochemistry2, University of Leipzig, Leipzig, Germany
Correspondence to: Catalina-Suzana Stingu
Institute for Medical Microbiology and Epidemiology of Infectious Diseases, University of Leipzig, Liebigstr. 21, Leipzig 04103, Germany
Tel: +49-3419715242 Fax: +49-3419715209 E-mail: CatalinaSuzana.Stingu@medizin.uni-leipzig.de
Received: September 23, 2016; Revised: January 12, 2017; Accepted: May 15, 2017; Published online: September 1, 2017.
© The Korean Society for Laboratory Medicine. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Two matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS)-based methods were compared for their ability to identify viridans streptococci. One approach employed a reference database and software developed in-house. All in-house measurements were performed using an Autoflex II Instrument (Bruker Daltonics GmbH, Germany). The other system, a VITEK-MS (BioMérieux, France) was operated on the commercially available V2.0 Knowledge Base for Clinical Use database. Clinical isolates of viridans streptococci (n=184) were examined. Discrepant results were resolved by 16S rDNA sequencing. Species-level identification percentages were compared by a chi-square test. The in-house method correctly identified 179 (97%) and 175 (95%) isolates to the group and species level respectively. In comparison, the VITEK-MS system correctly identified 145 (79%) isolates to the group and species level. The difference between the two methods was statistically significant at both group and species levels. Using the Autoflex II instrument combined with an extraction method instead of whole cell analysis resulted in more reliable viridans streptococci identification. Our results suggest that combining extraction with powerful analysis software and the careful choice of well-identified strains included into the database was useful for identifying viridans streptococci species.
Keywords: Viridans streptococci, MALDI-TOF MS, In-house database


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